Mansell carded five birdies and a single bogey to post the lowest round of the day and climb to 10 under par as strong winds and heavy rain made life difficult for the players at all three of this week's host courses.
Swede Alex Noren was alone in second place on eight under following his 69 at Kingsbarns, with Dane Niklas Norgaard Moller and Frenchman Antoine Rozner in joint-third after their 74s at St Andrews and Carnoustie respectively.
Australian trio Geoff Ogilvy, David Micheluzzi and Maverick Antcliff were all on two under, eight shots adrift, after respectively carding second round scores of 76,73 and 74.
Having opened his second round at the sixth hole due to the shotgun start at all three courses on Friday morning, Mansell made birdies at the seventh, ninth, 10th and 12th to catapult himself to the top of the leaderboard.
But as the conditions worsened, birdies were suddenly off the agenda and the battle to avoid losing ground became the priority.
Mansell bogeyed the 16th but pulled off some significant par saves elsewhere before notching a birdie at the fifth - his last - to head into the weekend with a two-stroke advantage.
Johannes Veerman & Will Ahmed and Christiaan Burke & Bruce Mitchell co-lead the team event on 19 under par.
Englishman Eddie Pepperell had a day to remember, making a magnificent hole-in-one at Kingsbarns' eighth hole.
He said: "It was just a good shot. It was a 6-iron, just trying to hold it up against a little bit of a right-to-left wind and it pitched online and just rolled down there, fed in. It was a good shot."
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